Tomato Leftovers Could Become a Smart Addition to Your Dog’s Bowl
If you’ve ever wondered whether tomato pomace is safe in dog food, a new feeding trial published in the journal Pets has some encouraging news. Researchers tested a tomato by-product — the skins, seeds, and pulp left over after tomatoes are processed into juice or sauce — in dog diets and found it was well tolerated. The dogs digested it at a high rate (above 90%), ate their food willingly, and showed no changes in body weight or how much they ate.
Tomato pomace is not a new concept in pet food research, but this study took an extra step: the pomace was specially pre-treated using enzymes and a vacuum drying method before it was added to the food. That processing step was designed to make the ingredient easier for dogs to digest. Based on the results from 12 healthy adult Beagles, it appears to have worked.
What Is Tomato Pomace, Exactly?
Tomato pomace is what’s left after tomatoes are crushed and pressed to make products like tomato paste, juice, or ketchup. It includes the skin, seeds, and some pulp — parts that most people would throw away. In large-scale food production, huge amounts of this material are generated every year.
Rather than sending all of it to landfill, researchers are looking at ways to turn it into useful ingredients for animal nutrition. Think of it like making stock from chicken bones after roasting a chicken — you’re getting more value out of something that would otherwise go to waste.
Tomato pomace is a source of dietary fiber and contains compounds from the tomato plant that may support gut health. But before it can be recommended in dog food, scientists need to check that dogs can actually digest it well and that they’ll eat food containing it.
How the Study Was Done
The research team designed a controlled feeding trial — a type of study where dogs are fed specific diets under carefully managed conditions, so researchers can compare the results fairly. They used a Latin-square design, which is a structured method that rotates which diet each animal receives, so every dog experiences each diet. This approach helps researchers separate out individual dog differences from the actual effects of the ingredient.
Twelve healthy adult Beagles took part in the trial. Each dog was fed a diet containing either no tomato pomace or diets with different amounts of it, and researchers measured:
- Digestibility — how much of the food the dogs’ bodies actually absorbed and used
- Palatability — whether the dogs were willing to eat the food (a key practical concern for any ingredient)
- Fecal characteristics — details about the dogs’ stool, which give clues about gut function
- Body weight and food intake — to check for any signs that the ingredient was harmful
What the Researchers Found
Dogs Digested It Well — Above 90%
The headline result is that dogs on diets containing tomato pomace showed digestibility above 90%. In nutrition science, that’s considered high. It means the dogs’ digestive systems were able to process the ingredient efficiently, and it wasn’t just passing through unused.
This matters because fiber-rich ingredients don’t always digest well. Some types of fiber ferment in the gut or cause loose stools. The high digestibility seen here suggests the pre-treatment method — using enzymes and vacuum drying — helped break the ingredient down in a way that was compatible with canine digestion.
Dogs Ate the Food Willingly
Palatability — whether dogs actually want to eat a food — is just as important as whether the food is nutritious. A food that dogs refuse to eat doesn’t help anyone. In this trial, the dogs’ willingness to eat was maintained across the diets, suggesting the tomato pomace did not make the food less appealing.
A 2% Diet Showed Some Gut-Health Signals
At the 2% tomato pomace level, researchers noted two changes in fecal measurements: a lower fecal pH and an increase in a compound called valerate. Fecal pH is a measure of acidity in the colon — lower pH is generally linked to a gut environment that may be less hospitable to harmful bacteria. Valerate is a type of short-chain fatty acid, a compound produced when gut bacteria ferment fiber. These signals suggest the ingredient may have had a modest positive effect on gut fermentation at that level, though the small sample size means this finding should be treated as early and exploratory.
No Harmful Effects Observed
Importantly, no adverse effects on body weight or food intake were seen across any of the diets. The dogs stayed healthy throughout the trial, with no signs that the ingredient was causing digestive upset or other problems.
Should You Change Your Dog’s Food Because of This Study?
This Study Does Not Change What You Should Feed Your Dog Today
It’s important to be clear: this is early research conducted on 12 healthy Beagles in a controlled setting. The study does not mean you should start adding tomato by-products to your dog’s homemade meals, and it’s not a signal that one specific commercial food is better than another.
What it does suggest is that tomato pomace — when properly processed — is a digestible, tolerated ingredient that could eventually show up in dog foods as a sustainable fiber source. If and when it does, this kind of feeding trial is exactly the evidence manufacturers need to show the ingredient is safe.
Sustainable Ingredients Are an Emerging Area of Pet Nutrition
Food by-products like tomato pomace represent a growing area of research in pet nutrition. As the global food system looks for ways to reduce waste, ingredients that were once discarded are being re-evaluated as nutritional resources. This study is part of that broader effort, and it shows that science — not guesswork — is the right way to test whether these ingredients belong in pet food.
Talking to Your Vet About Your Dog’s Diet
If your dog has a sensitive stomach, digestive issues, or a known food sensitivity, always talk to your vet before switching foods or trying new ingredients. Even ingredients that are generally well tolerated may not suit every individual dog.
If your dog is eating a balanced commercial diet and is doing well, there is no urgent reason to make changes based on this research. If you are curious about high-fiber dog foods or sustainable pet food options, your vet or a board-certified veterinary nutritionist can help you weigh the options for your specific dog.
Study Limitations
This trial was deliberately small, involving only 12 healthy adult Beagles. That means the results cannot automatically be applied to dogs of other breeds, ages, or health conditions. The study also does not establish that tomato pomace prevents any disease or provides specific health benefits beyond what was measured here. Larger, longer-term studies across more diverse dog populations would be needed before firm conclusions can be drawn.
What Owners Should Take Away
A new feeding trial found that tomato pomace — a by-product of tomato food processing — was well digested (above 90%) and well accepted by 12 healthy Beagles, with no harmful effects on body weight or food intake. A 2% level of inclusion also showed some gut fermentation signals that researchers consider promising. This suggests that properly prepared tomato pomace could be a viable, sustainable fiber ingredient in dog food, though more research with larger groups of dogs is needed to confirm these findings.
For now, the most important message for dog owners is that ingredient science in pet food is advancing — and that the best way to assess any new ingredient is through careful, controlled feeding trials like this one.
This article summarizes peer-reviewed research for educational purposes. Always consult with your veterinarian for personalized advice about your pet’s health and behavior.
